What’s the Difference?

‘‘ What’s the Difference The potential energy in a capacitor is stored in an electric field, where a between Batteries and battery stores its potential energy in a chemical Capacitors? form. The technology for chemical storage

’’ BATTERIES AND CAPACITORS seem similar as currently yields greater energy densities than they both store and release electrical capacitors. energy. However, there are crucial dif- ferences between them that impact their potential applications due to how they function differently. BATTERIES Pros Cons SUPERCAPACITORS Power Density Limited Cycle Life A capacitor consists of two or more Storage Capability Voltage And Current Limitations Better Leakage Current Than Capacitors Long Charging Times conductive plates separated by a dielec- Constant Voltage That Can Be Turned Off And On More Temperature Sensitive Than Capacitors tric. When an electric current enters the capacitor, the dielectric stops the flow CAPACITORS and a charge builds up and is stored in Pros Cons Long Cycle Life Low Specific Energy an electric field between the plates. Each Three packs of supercapacitors (in the blue package), consisting High Load Currents Linear Discharge Voltage capacitor is designed to have a particular of six D-size cells. Each 18 cells total were able to provide and Short Charging Times High Self-Discharge capacitance (energy storage). When a store the same amount of electrical energy as the smaller pack of Excellent Temperature Performance High Cost Per Watt capacitor is connected to an external six AA-size TLI 1550 Li-ion rechargeable batteries. circuit, a current will rapidly discharge. This table compares the pros and cons of batteries and capacitors

BATTERIES through a chemical reaction that gen-

Different battery types are distin- erates a voltage. The battery is able to DIFFERENCES battery because of this energy stor- guished by their chemical makeup. The produce a constant stream of electric- While batteries and capacitors age method. But unlike a battery chemical unit, called the cell, contains ity that can be turned on and off. In have similarities, there are sev- that can turn its electrical current three main parts: a positive terminal rechargeable batteries, the chemical eral key differences. The potential on and off, once a capacitor is con- called the cathode, negative terminal energy that is converted into electricity energy in a capacitor is stored in nected to an outside circuit it will called the anode, and the electrolyte. can be reversed using an outside electri- an electric field, where a battery discharge as fast as it can until all The battery charges and discharges cal energy to restore the charge. stores its potential energy in a the charge is drained. chemical form. The technology for While other differences exist, chemical storage currently yields batteries and capacitors do have PERFORMANCE BETWEEN SUPERCAPACITOR greater energy densities (capable some overlapping applications. COMPARISON AND LI-ION of storing more energy per weight) However, in general batteries Lithium-ion than capacitors. However, when provide higher energy density for Function Supercapacitor (general) a battery is discharging it can be storage, while capacitors have Charge time 1–10 seconds 10–60 minutes slower than a capacitor’s ability more rapid charge and discharge Cycle life 1 million or 30,000h 500 and higher to discharge because there is a capabilities (greater power densi- Cell voltage 2.3 to 2.75V 3.6 to 3.7V latency associated with the chemi- ty). The demand for fast portable Specific energy (Wh/kg) 5 (typical) 100–200 cal reaction to transfer the chemi- power has researchers trying to Specific power (W/kg) Up to 10,000 1,000 to 3,000 cal energy into electrical energy. A increase charging and discharging Cost per Wh $20 (typical) $0.50-$1.00 (large system) capacitor is storing the electrical times in batteries, while increas- Service life (in vehicle) 10 to 15 years 5 to 10 years energy directly on the plates so ing storage capacity in capaci- –40 to 65°C (–40 to discharging rate for capacitors are tors. While research continues to Charge temperature 0 to 45°C (32°to 113°F) 149°F) directly related to the conduc- improve batteries and capacitors, –40 to 65°C (–40 to tion capabilities of the capacitors there are still have distinct char- Discharge temperature –20 to 60°C (–4 to 140°F) plates. A capacitor is also able to acteristics that make each appli- 149°F) Source: Battery University discharge and charge faster than a cable to individual uses.